A battery is mounted in a vehicle such as an EV (Electric Vehicle) or an HEV (Hybrid Electric Vehicle) for supplying electric power to an electric motor. A plurality of storage cells that are connected in series are provided in the battery. Storage batteries such as nickel-metal hydride batteries or lithium ion batteries are used for storage cells. However, in order to use the storage batteries safely, the state of charge (SOC) of the battery needs to be monitored at all times so as to be controlled to prevent overcharge or over discharge. Note that the SOC of a battery is calculated based on accumulated values of charge and discharge currents and/or a terminal voltage of the battery. An error is included in the SOC (the control SOC) that is calculated based on this method, and there exists a deviation between the control SOC and the SOC in reality (the actual SOC).
In a monitoring system for monitoring the SOC of a battery mounted in a vehicle such as an HEV, the range of a control SOC where the battery can be used (a lower limit SOC to an upper limit SOC) is divided into a plurality of areas (hereinafter, referred to as “zones”) to monitor the battery. FIG. 8 is a diagram showing an example of a relationship between a range of a control SOC where a battery can be used and a plurality of zones thereof. As shown in FIG. 8, the range of the control SOC where the battery can be used is divided into four zones including Zone C, Zone B, Zone A and Zone D from the lower limit SOC side to the upper limit SOC side. Zone A is divided into three classes including Class L, Class M and Class H from the lower limit side to the upper limit side. Zone D is divided into two classes including Class L and Class H from the lower limit SOC side to the upper limit SOC side. A control unit for the battery executes the following controls depending upon the zone or class to which the control SOC of the battery belongs.
The battery in Zone C is in such a charged state that an internal combustion engine can be started by an electric motor (an engine start enabling state). Consequently, the control unit prohibits the discharge of the battery in Zone C but permits the discharge for starting the internal combustion engine by the electric motor. Additionally, the control unit prohibits an EV driving in which the vehicle is driven only by a driving force from the electric motor and an assist in driving the vehicle by the driving force of the electric motor. Note that the control unit prohibits totally the discharge of the battery whose control SOC is lower than a lower limit of Zone C (the lower limit SOC) and executes forced charging.
The battery in Zone B is in such a charged state that ensures the supply of electric power to the electric motor when the vehicle is climbing an uphill or starts (a hill climbing/start ensuring state). Consequently, the control unit prohibits the discharge of the battery in Zone B. Additionally, the control unit prohibits the EV driving and restricts the assist by the electric motor.
The battery in Class L in Zone A (hereinafter, referred to as “Zone AL”) is in such a charged stat (a sufficiently charged state) that permits the charge of the battery by driving the electric motor by the internal combustion engine and which restricts the EV driving (the driving based on the driving force from the electric motor only). Consequently, the control unit executes a standard control on a charge side on the battery in Zone AL. Additionally, the control unit restricts the EV driving and permits the assist by the electric motor.
Additionally, the battery in Class M in Zone A (hereinafter, referred to as “Zeon AM”) is in such a charged state that permits the charge of the battery by driving the electric motor by the internal combustion engine and which permits the EV driving (a flat or urban area general road driving enabling state). Consequently, the control unit executes a standard control on the battery in Zone AM. In addition, the control unit permits not only the EV driving but also the assist by the electric motor.
In addition, the battery in Class H in Zone A (hereinafter, referred to as “Zone AH”) is in such a charged state that restricts the charge of the battery by driving the electric motor by the internal combustion engine and permits the EV driving (a sufficient regenerative state with charge restricted). Consequently, the control unit executes a standard control on a discharge side on the battery in Zone AH. Additionally, the control unit permits the EV driving so as to enhance the assist by the electric motor.
The battery in Class L in Zone D (hereinafter, referred to as “Zone DL”) is in such a charged state that restricts the charge of the battery by driving the electric motor by the internal combustion engine (a discharge side enlarging state with charge restricted). Consequently, the control unit restricts the charge of the battery in Zone DL. Additionally, the control unit enhances the EV driving and the assist by the electric motor.
In addition, the battery in Class H in Zone D (hereinafter, referred to as Zone DH”) is in such a charged state that prohibits the charge of the battery by driving the electric motor by the internal combustion engine and restricts the regenerative operation of the electric motor during deceleration (an overcharge and lack of deceleration preventing state). Consequently, the control unit prohibits the charge of the battery in Zone DH and restricts the regeneration thereof. Note that the control units prohibits the charge and regenerative operation of the battery whose control SOC is higher than an upper limit of Zone DH (the upper limit SOC) and discharges the battery in a forced fashion.